The packet domain of modern communication systems uses packet-mode techniques to transfer user data and signaling in an efficient manner. Strict separation between the radio subsystem and network subsystem is typically maintained, which allows the network subsystem to be shared by several radio access technologies.
The air interface of the radio system, on the other hand, allows signals from many users to be multiplexed over the same physical resource. Resources are given to a user upon need and are reallocated immediately thereafter. In order to accomplish this, the radio access network comprises functional elements for controlling the use of the air interface. In order to be able to appropriately control the radio resources, these functional elements need diverse cell-specific information on cell-specific groups of other cells. For circuit switched functions the specifications define exhaustively data transfer and information exchange procedures, which ensure that valid and relevant information is provided timely for the functional control elements. However, in the packet domain, some problematic deficiencies have been identified.
For example, a Network Assisted Cell Change (NACC) function reduces the service outage time at cell reselection. NACC allows support to be given to the mobile stations as system information for the target cell before the mobile station performs the cell reselection. In order to be able to provide NACC, a functional unit handling the handover of a mobile station from a source cell to a target cell needs a certain set of system information messages of the target cell. 3GPP specifies a RAN Information Management (RIM) procedure that allows delivery of information between Radio Access Network (RAN) nodes transparently to the core network. However, RIM procedures are routed via the core network, and incurring of additional load and thus increasing the risk of congestion of the interface between the radio system and the network system should be carefully avoided.
As another example, the 3rd Generation Partnership Program (3GPP) standards further define network controlled cell reselection (NCCR) procedure, wherein a cell reselection is initiated for an individual mobile station by the network. In general, cell-specific load reports are delivered in specific types of circuit switched handover messages. Based on this information, load information would be available for the purpose of load-based cell reselection only in cases where the mobile station has had circuit switched connection with handovers between cells. Such dependency of packet domain operations on the circuit switched operations is not acceptable. Some advanced base station controllers allow checking of target cell loads and resource availabilities before a controlled cell change order is given. This is, however, possible only when the source and the target cells are controlled by the same base station controller. The information is equally needed in other configurations, as well.